Briskness (5)
'briskness' is the definition.
(I know that briskness can be written as alacrity)
This is all the clue.
(Other definitions for alacrity that I've seen before include "Prompt and eager readiness" , "Brisk and cheerful readiness" , "'Quick, cheerful enthusiasm (8)'" , "Enthusiasm; speed" , "Quickness" .)
'briskness' is the definition.
(thesaurus)
This is the entire clue.
(Other definitions for haste that I've seen before include "''More . . . . ., less speed'' (5)" , "Heats (anag.)" , "velocity" , "Possible cause of careless mistakes?" , "The more of it, the less speed sometimes" .)